Testing Older Panels for Efficiency/Worth Installing

CBear42CBear42 Solar Expert Posts: 28
My new 1Kw system went in last weekend and it's working wonderfully. However, based on what the solar vendor told me, I was hoping to eke some further use out of my older panels. It would have brought my system to an almost 1.5Kw system - and we all know that more wattage tends to be a "good" thing. The panels were manufactured in 1996 according to the date on the panel itself. The NYSERDA certified installer told me that the panels worth not worth re-installing. That they had lost 80% of their collection capacity.

Does anyone here know if that great a drop in capacity is a normal outcome of an old panel - or can some use still be made of these panels? How do I test for how much I can really get out of them? I live 1/2 mile from the Canadian border in northern New York and do have some shade and building addition "issues".

Thanks very much in advance for your input!

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Testing Older Panels for Efficiency/Worth Installing

    Most of us have seen no appreciable drop in panel output over time, contrary to what has been predicted. You can always test the panels for short-circuit current in full sun and see how close they come to specs.

    I'm a bit concerned about the way you've expressed your system capacity: "1kW system". Is this a 1kW array charging batteries? If it is a tiny GT system you really should not be adding panel as the design would not have been approved with the additional capacity.

    Adding panels is not always as easy as just hooking more up, either. The charge controller has to be able to utilize the extra current potential and the panel specs have to be close enough to that of the existing array's. Otherwise you add them with another controller.
  • peakbaggerpeakbagger Solar Expert Posts: 341 ✭✭✭
    Re: Testing Older Panels for Efficiency/Worth Installing

    I have some 1990 vintage Siemens panels, they originally tested out as 65 watts and have some EVA delamination so are not perfect and they still put out 55 to 60 watts.

    I expect its more like the installer doesn't want to deal with them, he probably has a standard design and the old panels will not integrate with it. I expect with a 1 Kw system, its set up with micro inverters as not many companies make 1 KW grid tie units these days. The economics of microinverters are that you want to maximize the panel wattage to line up with the microinverter rating. I would expect your older panels are considerably less wattage than the current Enphase units and I am not sure if you can have two panels on one enphase.
  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: Testing Older Panels for Efficiency/Worth Installing

    If he told you they had lost 80%, then he does not know what he is talking about. I have seen panels over 30 years old that still put out over 90%.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Testing Older Panels for Efficiency/Worth Installing
    Windsun wrote: »
    If he told you they had lost 80%, then he does not know what he is talking about. I have seen panels over 30 years old that still put out over 90%.

    If they were amorphous thin film panels which had been sitting out in the sun continuously, then the loss might be a lot more, but even then probably not down to 20%.
    SMA SB 3000, old BP panels.
  • CBear42CBear42 Solar Expert Posts: 28
    Re: Testing Older Panels for Efficiency/Worth Installing

    My apologies if I was unclear about my current setup.

    There was an older solar system in this house when I purchased it. It was unusable - the batteries were shot, and everything was replaced. I now have 4-250w panels using an Outback 3500w inverter with a new battery bank of 4-250 Amp AGM batteries. This is working well although since we've had no sun due to Sandy - it's difficult to tell how the panels are truly performing right now. I purchased everything from Grape Solar and had a certified installer install everything. Originally, Grape said that I might be able to get some use from the older panels - so, a separate charge controller was purchased for them.

    During the day of the installation, it was discovered that the new panels would not physically fit on the metal roof. So, we removed the old panels from the pole mount and installed the new panels there. It was at that time that the installer said he had tested them and found they were "shot". This was disappointing because I had really hoped to get some use from them - but I didn't know how old they were. I also didn't know if the technology in 1996 had the longevity we see today. The installer said that panels can last from 20-25 years - but that after 15 years there is a precipitous decline in their collectiing capacity and efficiency.

    That was the reason for the original post. My question is, then, - how do I test these panels to see what their true capacity and state might be at this time..?

    Thank you all for your responses - they truly are helpful.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Testing Older Panels for Efficiency/Worth Installing

    To test the panels you need:

    1). Bright sun or the equivalent in artificial lighting
    2). A DC Ammeter capable of reading the potential maximum current

    You put the panels square-on to the bright sun and read the short circuit current (one at a time) with the meter. Since panels are a current source this is what is most important. Voltage alone won't tell you anything; it is possible to have proper Voc with just a little light and yet the panels will produce no significant current. There is another spec of shunt resistance but that's not easy to measure or particularly vital as a first test.

    If you don't have the actual specs on the panels you can approximate the current by dividing the Watt rating y 17.5 (typical Vmp for "12 Volt" panels).
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Testing Older Panels for Efficiency/Worth Installing

    do definitely check each pv individually. i would not take the word of the installer to blanket all of the pvs as being shot as it could be a number of things going on. he may be accurately referring to the old pv system as a whole as being shot. even if you find a few good ones, use them with your separate new cc. if none are any good then you have a back up cc.

    do you know what the make and model number of the old pvs are?
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